The present invention relates to a lock assembly for automatically dead bolting a closure to a closure frame when the ambient temperature is raised above a predetermined temperature by, for example, a fire. Assemblies of this type are known as fire safety locks and are most commonly used on fire safety doors.
In order to isolate a dangerous fire and resulting smoke, many modern buildings are divided into discreet, fire-tight compartments which are usually coextensive with a room or group of rooms. In order to maintain the integrity of each compartment, the doors which lead to and from it should be essentially fire proof and should be positively locked or "dead bolted" in a closed position to adequately contain a fire when one occurs. Moreover, since fire safety doors often provide access to rooms which are ordinarily in everyday use, the fire safety locks on them should function smoothly and easily in the absence of an emergency.
In the past, ensuring that fire safety doors stay closed and locked once a fire reaches certain proportions has been a major problem. Such doors usually warp severely under the intense heat, up to 1000.degree. F, generated by some fires. Furthermore, sudden cooling which occurs when fire doors are sprayed with water from an automatic sprinkler system or from a fire fighter's hose, causes the door to warp even more. This warping causes extreme stress to be placed on the door lock which may consequently burst or be forced to unlatch or otherwise fail. Of course, if the lock fails, the fire safety door can open and can, thus, no longer contain or confine the fire.
Therefore, it is advantageous to equip fire safety doors with locks which automatically dead bolt the doors closed when fire strikes.
It is also important that an automatic fire safety lock does not operate accidentally to dead bolt a door which is in common use. If such an accident occurs, access through the door is cut off and a locksmith may have to be called to free the lock. Even more importantly, however, an automatic fire safety lock should only operate to dead bolt a safety door at a relatively high temperature. If this is not the case, people may be trapped in fire-tight compartments with little hope of escape while a fire intensifies.